Method for manufacturing vapor deposited electrode

ABSTRACT

A method for manufacturing secondary emission electrode deposited on a thin supporting film by vacuum evaporation, wherein a rigid body is arranged adjacent to a surface of the thin film opposite to the vaporizing surface. The opposite surfaces of the rigid body and the thin film may be arranged in parallel and at a distance, for example, about 0.05 mm or they may be so arranged to increase the distance at locations radially more distant from the central portion of the thin film. An evaporating material is vapor deposited onto the supporting surface, thus a secondary emission electrode layer having a uniform thickness can be obtained.

United States Patent 1191 Toyonaga et al.

1 1 June 25, 1974 METHOD FOR MANUFACTURING VAPOR DEPOSITED ELECTRODE [75] Inventors: Ryuya Toyonaga, Ebina-Machi;

Eikyu Hiruma, Tokyo, both of Japan [73] Assignee: Nippon Hoso Kyokai, Tokyo, Japan [22] Filed: Mar. 27, 1972 [21] Appl. N0.: 238,513

[30] Foreign Application Priority Data May 27, 1971 Japan 46-36498 52 US. 01. 117/201, 117/7, 117/106 R, 117/106 A, 117/106 c,117/107,117/107.1, 117/107.2 R, 118/48, 118/49, 118/49.l, 118/496 51 1111. C1. B44d 3/18, B446 l/18 [58] 51 111 of Search, 117/201, 106 R, 107, 107.2 R, 117/107.1, 106 A, 106 c; 118/48-49.5, 117/7 [56] References Cited UNITED STATES PATENTS 2,527,747 10/1950 Lewis 118/49 3,100,723 8/1963 Weed 118/49 3,326,717 6/1967 Gregor 118/49 3,636,919 l/1972 Bozler 118/48 Primary Examiner Leon D. Rosdol Assistant Examiner-Michael F Esposito Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [57] ABSTRACT A method for manufacturing secondary emission electrode deposited on a thin supporting film by vacuum evaporation, wherein a rigid body is arranged adjacent to a surface of the thin film opposite to the vaporizing surface. The opposite surfaces of the rigid body and the thin film may be arranged in parallel and at a distance, for example, about 0.05 mm or they may be so arranged to increase the distance at locations radially more distant from the central portion of the thin film. An evaporating material is vapor deposited onto the supporting surface, thus a secondary emission electrode layer having a uniform thickness can be obtained.

6 Claims, 10 Drawing Figures PATENTEDMIZSIW SHEU 1 [If 4 PATENTEDJHN25I974 3,819,408

SHEET 2 OF 4 LAYER THICKNESS DISTANCE FROM EDGE (mm) 1 METHOD FOR MANUFACTURING-VAPOR DEPOSITED ELECTRODE BACKGROUND OF THE INVENTION 1. Field of the Invention The present inventionrelates to a methodiformanufacturing vapor deposited electrodes in whicha porous electrode layer'is'formed ona1-thin" supporting film ina vacuum chamber by vaporization; Moreparticularly,

the present invention'relates to amethod for manufacturing vapor deposited electrodes whichis able'to form a vapor deposited electrode layer having a substantially uniform thickness.

2. Description of thePrior Art Heretofore, there has been proposeda method: for forming a vapor depositedelectrode layer on a thinsupporting film, in' which the thin supporting film is stretched and is supported with'ametal frame and the thus supported thinfilm is placed andnfi'xedin-an evaporation chamber where a' desired evaporating material sembly (l, 2) is held on' a rotarysupporting plate 4 in a'bell jar 3 of an evaporator. as shown in FIG; 2"...

Next, air in the bell jar 3' is exhaustedfroman outlet 6 through a main valveS and thereafter, argon or nitrogen gas is introduced thereinto from an inlet 7'through an inlet valve 8 so as to maintain the inert gasatmosphere in a vacuum of about I to 2' Torr. A sintered body of cryolite and magnesium oxide (Na AlF MgO) is previously charged into an evaporating source 9. in the bell jar 3 andthen evaporatedby heating so as to deposit a porous secondary electron. multiplier target on the surface of the film.

In FIG. 2, 10 represents a motor for driving the rotary supporting plate 4.

The vapor deposited layer 11 obtained by the above mentioned conventional method shown in FIG. 3ihasa disadvantage that the thickness of the obtainedlayeris not uniform and it has the most thin portion at center of the film 2 and becomesthicker from the centralportion toward the circumference of the filmv 2. or the metal frame 1. In some cases, there. will be the further disadvantage that no vapordeposited layer is formed on the central portion of the film 2.

Such a phenomenon is troublesome in the manufacture of camera tubes as explained below. Namely, when.

such a vapour deposited layer having an uneven thickness is used as a secondary electron multiplier target for a secondary electron conduction type camera tube,

the secondary electron gain, the dark current and the afterimage time are different in the central portion and in the surroundings of the vapor'deposited layer, so that an unevenness of sensibility is caused and it is difficult to operate the whole surface of thetarget in a: high gain; and further an improvement of performance of the camera tube cannot be expected.

F IG. 4 shows experimental results with respect to the ununiformity of the thicknes' of thevapor deposited layer: obtainedby the conventional method, wherein the. evaporating. material consisting of cryolite'magnesium oxide. (Na AlF 'MgO) is deposited on the signal electrode film consisting mainly of aluminium to form the secondary electron multiplierv target.

In" this"; figure, an' ordinate; shows the thickness (am) of the.-:secondary electron multipliertarget, that is, the vapor 'depositedilayer, while. an-abscissa shows the distance (mm?) from one side of the circular signal electrode; film: having a diameter of l8 mm, i.e. the electrode supporting film.

Tlievariation of the thickness of the vapor deposited Iayer-isindicatedby curved lines connecting symbols A,

x and.0 with respect to the supporting-film having the thicknes of 4,650 A., 2,650 A. and 650 A., respectively.

As seen from FIG. 4, there is a tendency that the thicker the thickness of the supporting film, the more the uniformity of the vapor deposited layer is improved.v

For instance, inv case of a secondary electron multiplier target for. acamera tube, however, the transmis-,

sion loss of photoelectron increases as the supporting filmbecomes thicker, so that it is necessary to use a sufficiently thin supporting film.

In the conventional method, there are disadvantages as describedabove when a target electrode for a camera. tube isformed by. vapor deposition, so that it was very difficult to manufacture a vapor deposited electrode having a. uniform thickness.

Although the causes for said tendency are not clarified, thefollowing may be considered: the thermal conduction around the target supporting film is comparatively high because the circumference of the supporting film is provided with an annular rigid frame, while the thermal conduction in the central portion of the supporting film is low because at the central portion there is only a thin supporting film having a thickness of about 500 to 2,000 A. Therefore, the temperature rises at the central portion of the supporting film and the target material. is scarcely deposited on the said central portion, or since the target supporting film is very thin as described above, a collision of heated gas molecules or particles of evaporating material is caused by convection of atmospheric gas during the evaporation, whereby the film is particularly vibrated at its central portion, and hence comparatively less target material is vapor deposited on the said central portion.

It has been experimentally confirmed that said tendency occurs not only when evaporating a target material or-secondary electron multiplier material such as Na AlF 'MgO and the like but also with other metals suchasaluminium, magnesium, etc. in an inert gas atmosphere, or when evaporating metalssuch as magnesium and thelike under high vacuum.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing vapor deposited electrodes,

inv which a vapor deposited layer having a uniform thickness is evaporated on a'sufficiently thin supporting film being capable of causing the above mentioned phenomenon.

Another object of the present invention is to provide a method for the manufacture of secondary electron multiplier targets, in which a thin film working as a signal electrode is used as a supporting film and a vapor deposited layer consisting of a secondary emissive material can easily be formed thereon in a uniform thickness.

The present invention is fundamentally the improvement of the conventional method for manufacturing a vapor deposited layer on a supporting film by vapor deposition.

The present invention has been obtained based on the recognition of such production of unevenness of vapor deposited electrodes in the conventional method for manufacturing secondary electron multiplier target by vapor deposition as described above. In accordance with the present invention, a rigid body having low gas discharging characteristics, such as copper or glass is arranged in close proximity of the back surface opposite to the vapor depositing surface of the signal electrode film and vapor deposition is carried out in this assembled state, whereby the vapor deposited layer can be formed to be thicker on the surface of the supporting film opposite to the area close to the rigid body in other portions.

The present invention provides a method for manufacturing vapor deposited electrode comprising steps of oppositely arranging an evaporation source for evaporating electrode material and a thin supporting film on the front surface of which said electrode is vapor deposited in an evaporating chamber, providing a back cover made of a rigid body in close proximity of the rear surface of the thin supporting film, evaporating said electrode material, and vapor depositing said evaporated electrode material onto said front surface of the thin supporting film to form a vapor deposited electrode.

According to the present invention, it is an advantage that the thickness of the vapor deposited layer can be varied depending upon the relative distance between the back cover and the thin supporting film. Thus, by making the back cover in a proper form, vapor deposited layers having not only a uniform thickness but also any desired configuration can easily be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS For better understanding of the invention, reference is made to the accompanying drawings, in which:

FIG. 1A is a front view showing an embodiment of a thin supporting film to have a vapor deposited layer formed thereon;

FIG. 1B is a cross-sectional view of the thin supporting film taken on the line X-X in FIG. 1A;

FIG. 2 is a perspective view of an evaporating apparatus used for practicing a conventional vapor deposition method;

FIG. 3 is a crosssectional view illustrating a deposition state of a porous layer on the thin supporting film according to the conventional method;

FIG. 4 is a graph showing a relation between the thickness of the thin supporting film and the thickness of the target layer (porous layer) deposited thereon according to the conventional method;

FIG. 5 is a cross-sectional view illustrating the deposition state of the porous layer according to the present invention;

FIG. 6 is a graph showing the variations of thickness of the porous target layer deposited on the thin supporting film having a thickness of 650 A according to the present method and the conventional method;

FIG. 7 is a cross-sectional view of an embodiment of a back cover used for illustrating the effect of the present invention;

FIG. 8 is a graph showing the thickness of the target layer (porous layer) obtained by using the back cover of FIG. 7; and

FIG. 9 is a cross-sectional view of an embodiment of the back cover to be used in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 5, 1 represents an annular rigid supporting frame made of, for example, nichrome material and 2 represents an electroconductive metal film adhered to the supporting frame 1 in a stretched state by any well-known means. For instance, in the manufacture of a target for a camera tube, a metal film consisting mainly of aluminium, or an alumina film formed by depositing aluminium on a signal electrode film, or an aluminium metal film reinforced with a net with small meshes may be used.

Generally, said thin supporting film 2, on which a vapor deposited layer is formed, is retained in a stretched state with the supporting frame 1 as previously explained with respect to FIGS. 1A and 1B.

According to the present invention, a rigid body 10 such as metal, glass or the like, used as a back cover is arranged in 'close proximity with the back surface opposite to the surface of the thin film 2 having the vapor deposited layer formed thereon. This assembly (1, 2, 10) is placed on a fixed or rotary supporting plate 4 in a conventional evaporating apparatus as shown in FIG. 2. In this case, the vapor depositing surface of the thin supporting film 2 is faced to an evaporating source for a target material 9 through holes provided in the supporting plate 4.

The present invention will be explained by taking an example that a porous vapor deposited layer having a uniform thickness is formed on the surface of the thin supporting film as a secondary electron multiplier electrode for camera tube. A sintered body consisting of cryolite (Na AlF and magnesium oxide (MgO) in a weight ratio of l 1 is, for example, used as an evaporating material and charged into the evaporating source 9. Then, a main valve 5 is opened and air in a bell jar 3 is exhaustd from an outlet 6. After evacuation of the bell jar 3 in high vacuum, the main valve 5 is closed, while an inlet valve 8 is opened and an inert gas such as argon or nitrogen is introduced into the bell jar 3 through an inlet 7. When the inside of the bell jar 3 reaches a pressure required for evaporation, for example, about 1 to 2 Torr, the inlet valve 8 is closed. Thereafter, an electric current is passed through a heater element of the evaporating source 9 for the target mate rial to raise the temperature, whereby the target material is evaporated and deposited to form a target layer 12 on the surface of the thin supporting film 2 facing the evaporating source 9 as shown in FIG. 5. In this case. the target layer 12 becomes porous because the evaporation is carried out in the inert gas atmosphere. In this figure, 13 represents a small aperture for escaping gas.

The thickness of the porous vapor deposited layer formed on the thin supporting film by the above mentioned method was measured at the central portion and Distance between target Thickness of target layer supporting film and back cover central portion circumference no back cover 6 am 25 um close proximity 20 pm 20 pm 0.1 mm 20 pm 20 pm 0.3 mm 20 pm 20 um 1.0 mm run 25 pm As seen from the above table, the target layer can be deposited without unevenness of the thickness when the back cover is arranged in proximity or close to the back surface of the thin supporting film. Thus, in order to obtain a vapor deposited layer having a uniform thickness, it is necessary to arrange the back cover over back surface of the thin supporting film. Furthermore, if the distance between the back cover and the thin supporting film is adequately set in connection with the position of the thin supporting film, it is easy to vary the thickness of the vapor deposited layer having desired uniformity.

In order to make the effect of the present invention more clear, FIG. 6 shows a result measured with respect to the thickness of the vapor deposited layer formed on the thin supporting film of 650 A. thick. A curved line denoted by symbol 0 is the case of the conventional method and that of symbol x is the caseof the present invention. As seen from this figure, the vapor deposited layer having a uniform thickness can be easily formed according to the present invention using the back cover, while in the conventional method the central portion and thecircumference of the vapor deposited layer are considerably different in thickness and it is impossible to obtain a vapor deposited layer having a satisfactorily uniform thickness.

In order to prove the above mentioned fact, the central portion of the back cover 14 is provided with an aperture having a diameter of 3 mm or 6 mm as shown in FIG. 7. Then, a vapor deposited electrodelayer is manufactured by usingthe perforated backcover 14 in the same manner as described above exceptthatthe distance between the back cover and the. thin supporting film is 0.1 mm. The thickness of the thus vapor depos+ ited electrode layer was measured to obtain a result as shown in FIG. 8.

In this figure, an ordinate is the thickness of thevapor deposited electrode layer, and an abscissa is the distance from one side of the vapor deposited electrode supporting film having a diameter of 18 mm. A curved line of symbol 0 shows a result obtained by using the back cover with the aperture of 3 mm dia., and that of symbol x shows a result obtained by using the back cover with the aperture of 6 mm dia.

As seen from FIG. 8, thetarget layer deposited on the supporting film corresponding to thearea of theaperture is thinner than that corresponding to the area of the back-cover. Namely, it can be seen that when using the back'cover according to the present invention, the deposition amount at the central portion, which is apt to be lacking in the conventional method, may easily be increased and consequently unevenness of the thickness in the vapor deposited layer can be eliminated.

The present invention is not intended to be limited to the above mentioned embodiments, and it will be understood by those skilled in the art that many modifications and variations thereof may be employed without departing. from the scope of the invention. For instance, if the thin electrode supporting film is reinforced with a mesh or the like and is provided sufficient strength and thermal conductivity, the back cover may be made in a convex form so that the central portion is located closer to the said thin supporting film than the circumference thereof as shown in FIG. 9. As a practical embodiment, evaporation treatment is carried out in the same manner as described above, while arranging the center distance between the back cover and the thin supporting film to be 0.1 mm and to be 1 mm at the circumference, the obtained thickness of the vapor deposited-electrode layer is 20 pm at the central portion and 18 pm at the circumference thereof. This shows that a vapor deposited layer having a uniform thickness can be deposited on the thin supporting film by making the surface of the back cover facing the thin supporting film in an adequate shape depending upon the nature and strength of the thin supporting film and desired thickness of the vaporized electrode. A great advantage can be obtained by this specific feature of the present invention.

According to this particular feature, it is possible to obtain a target electrode formed on a thin film by vapor deposition having a predetermined pattern, such as provided with lines or dots target so as to generate secondary electrons to a certain extent by properly arranging a corresponding pattern on the back cover in concave or convex form thereon and selecting the depth thereof appropriately. When using such a patterned back cover, a target electrode layer having the same pattern to that of the back cover, the thickness of which is varied according to the pattern, can easily be obtained.

The above explanation is made with respect to the example formanufacture of the vapor deposited layer using cryolite and magnesium oxide as an evaporating material, but the present invention is not limited only to such evaporating materials. In brief, the present invention lies in that the vapor deposited layer having uniform thickness or any desired shape can easily be obtained by arranging the back cover in proximity with the thin supporting film to be provided with a deposition layer and applying the vapor deposition.

For instance, in the manufacture of target electrodes for secondary electron conduction type (SEC-type) vidicon tubes, electron image multipliers and the like, a light absorption layer having a unifonn thickness, for example, a black aluminium layer, is deposited on the surface opposite to the vapor depositing surface of the target electrode supporting film in an inert gas atmosphere according to the present invention, and then the target electrode layer is formed on the deposition surface of the supporting film as described above. When thethus obtained target electrode is integrated in the above mentioned electronic tube, light passing through the photoconductive surface is absorbed by the target electrode supporting film and is not reflected. Therefore, there is no degradation of resolution and contrast based on the secondary emission due to reincidence of reflected light to the photoconductive surface caused by using a target electrode supporting film having a glossy surface. Furthermore, since the thickness of the obtained target electrode is uniform, electronic tubes of the above mentioned type having excellent and sufficiently even properties in secondary electron gain, dark current, afterimage and the like can be manufactured.

According to the conventional vapor deposition method, it has been difficult to deposit a porous black aluminium layer on a target electrode supporting film because the supporting film is very thin, while according to the present invention the black aluminium layer can be easily formed because it deposits the evaporating material on the portion of the thin supporting film adjacent to the back cover as previously explained.

Alternatively, when magnesium is deposited under high vacuum and oxidized to form an MgO target for an image orthicon of high lifetime, if the back cover of the present invention is used, a very homogeneous magnesium deposit layer having uniform thickness can be formed on the thin supporting film.

Moreover, it is obvious that the present invention is applicable to a method of manufacturing vapor deposited electrode layers required for various purposes in uniform thickness on the supporting thin film.

According to the present invention, by arranging back cover in the proximity or close to the thin supporting film, deposition of the evaporating material on the undesirable side of the thin supporting film is prevented, and at the same time even if the thin supporting film is very thin, the vapor deposited layer having desirable uniform thickness can be deposited on the desired side of the thin supporting film. Especially, it is advantageous that when a porous layer is to be used as a target layer, such target electrodes having excellent properties in secondary electron gain, dark current, afterimage time and the like can be obtained.

What is claimed is: l. A method for manufacturing a vapor deposited porous electrode layer, comprising:

stretching a thin supporting film for said electrode on a rigid frame,

arranging a back cover comprising a rigid body spaced adjacent the rear side of said supporting film at a distance of less than about 0.3 mm in an evaporator,

evaporating electrode material from an evaporation source at the front surface of said supporting film, while maintaining said back cover spaced adjacent the rear side of said film, thereby forming a porous layer of said electrode material of substantially uniform thickness on the front surface of said film.

2. A method for manufacturing a vapor deposited electrode as claimed in claim 1, wherein said film is about 300 A. thick.

3. A method for manufacturing a vapor deposited electrode as claimed in claim 1, wherein said film is about 650 A. thick.

4. A method for manufacturing a vapor deposited electrode as claimed in claim 1, wherein the surface of the back cover facing the thin supporting film is convex toward said film.

5. A method for manufacturing a vapor deposited electrode as claimed in claim 1, wherein the back cover is provided with at least one small aperture for allowing gas present between the back cover and the thin supporting film to escape.

6. A method for manufacturing vapor deposited electrode as claimed in claim 1, wherein a surface of the back cover facing the rear surface of the thin supporting film is flat. 

2. A method for manufacturing a vapor deposited electrode as claimed in claim 1, wherein said film is about 300 A. thick.
 3. A method for manufacturing a vapor deposited electrode as claimed in claim 1, wherein said film is about 650 A. thick.
 4. A method for manufacturing a vapor deposited electrode as claimed in claim 1, wherein the surface of the back cover facing the thin supporting film is convex toward said film.
 5. A method for manufacturing a vapor deposited electrode as claimed in claim 1, wherein the back cover is provided with at least one small aperture for allowing gas present between the back cover and the thin supporting film to escape.
 6. A method for manufacturing vapor deposited electrode as claimed in claim 1, wherein a surface of the back cover facing the rear surface of the thin supporting film is flat. 